Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financial information for operating segments
Net interest income	$ 72,351	$ 68,612	$ 51,614	$ 48,781	$ 49,967	$ 50,427	$ 52,138	$ 49,950	$ 241,358	$ 202,482	$ 157,133
Provision for loan losses	1,750	750	1,175	1,075	1,050	2,217	1,450	1,450	4,750	6,167	10,350
Noninterest income	31,442	32,079	22,879	21,870	19,941	22,531	19,443	18,594	108,270	80,509	71,891
Noninterest expense	70,734	75,979	51,082	47,319	45,900	48,098	49,337	47,602	245,114	190,937	172,928
Income before income taxes	31,309	23,962	22,236	22,257	22,958	22,643	20,794	19,492	99,764	85,887	45,746
Income taxes	10,149	7,742	6,842	7,017	7,361	7,108	5,941	5,895	31,750	26,305	12,259
Net income	21,160	$ 16,220	$ 15,394	$ 15,240	15,597	$ 15,535	$ 14,853	$ 13,597	68,014	59,582	33,487
Total assets	7,926,496				5,805,129				7,926,496	5,805,129	5,746,270
Goodwill	445,871				274,706				445,871	274,706	276,100
Community Banks
Financial information for operating segments
Net interest income									244,242	205,353	158,322
Provision for loan losses									4,752	6,249	10,219
Noninterest income									88,498	61,973	58,648
Noninterest expense									228,248	175,660	160,704
Income before income taxes									99,740	85,417	46,047
Income taxes									32,941	27,037	13,036
Net income									66,799	58,380	33,011
Total assets	7,833,084				5,720,995				7,833,084	5,720,995	5,671,428
Goodwill	443,104				271,939				443,104	271,939	273,343
Insurance
Financial information for operating segments
Net interest income									311	237	135
Provision for loan losses									0	0	0
Noninterest income									9,340	9,055	5,619
Noninterest expense									6,900	6,441	4,268
Income before income taxes									2,751	2,851	1,486
Income taxes									1,078	1,114	575
Net income									1,673	1,737	911
Total assets	22,550				20,472				22,550	20,472	17,312
Goodwill	2,767				2,767				2,767	2,767	2,757
Wealth Management
Financial information for operating segments
Net interest income									1,688	1,332	1,275
Provision for loan losses									(2)	(82)	131
Noninterest income									10,559	8,997	7,552
Noninterest expense									9,130	8,111	7,133
Income before income taxes									3,119	2,300	1,563
Income taxes									0	0	0
Net income									3,119	2,300	1,563
Total assets	46,035				44,275				46,035	44,275	44,360
Goodwill	0				0				0	0	0
Other
Financial information for operating segments
Net interest income									(4,883)	(4,440)	(2,599)
Provision for loan losses									0	0	0
Noninterest income									(127)	484	72
Noninterest expense									836	725	823
Income before income taxes									(5,846)	(4,681)	(3,350)
Income taxes									(2,269)	(1,846)	(1,352)
Net income									(3,577)	(2,835)	(1,998)
Total assets	24,827				19,387				24,827	19,387	13,170
Goodwill	$ 0				$ 0				$ 0	$ 0	$ 0